JPH07173785A - Method for bleaching peroxide or ozone in chemical pulp - Google Patents

Abstract

(57) [Summary] [Object] To provide a chemical pulp having a low Kappa number and a high whiteness in a peroxide or ozone bleaching method of the chemical pulp. [Structure] Before bleaching a chemical pulp with peroxide or ozone, the delignification reaction is promoted by the enzyme by the simultaneous treatment with the enzyme and the chelating agent in one step, or in each of the two steps. Trace metals are removed. [Effect] Compared with the conventional peroxide or ozone bleaching method, a chemical pulp having a low Kappa number and a high whiteness can be obtained.
Furthermore, since there is no chlorine drainage in the previous stage, not only is the drainage load reduced, but it also leads to the reduction of environmentally problematic organic chlorine compounds. It is also possible to reuse white water.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for bleaching chemical pulp with peroxide or ozone. More specifically, in the peroxide or ozone bleaching of chemical pulp, the delignification reaction is carried out by a bleaching pretreatment consisting of a one-step treatment in which an enzyme and a chelating agent are mixed and treated, or a two-step treatment in which they are individually treated. Is a peroxide or ozone bleaching method for chemical pulp, which is characterized in that

[0002]

2. Description of the Related Art The purpose of pulp bleaching is to remove lignin and coloring substances adhering to the inside and the surface of pulp fibers by decomposing, altering or dissolving them to increase the whiteness.

Conventionally, the bleaching of pulp has been performed by a stepwise treatment with chlorine, hypochlorite, hydrogen peroxide, hydrogen dioxide or the like. In recent years, an oxygen bleaching method has been widely adopted for the purpose of reducing the load of waste water and reducing the cost of bleaching chemicals.

On the other hand, recently, AO containing dioxin
From the viewpoint of X regulation and safety, do not use chlorine-based chemicals,
So-called chlorine-free bleaching methods have been developed and put into operation. Non-chlorine bleaching methods include a TCF method that does not use chlorine and chlorine dioxide and other chlorine-based chemicals at all, and an ECF method that does not use chlorine alone.

The chlorine-free bleaching method with peroxide and ozone is already known. However, in peroxide or ozone bleaching, unless the pulp has been pretreated,
Peroxide or ozone present in pulp slurry M
Since it is decomposed by trace metals such as n and Fe and the bleaching efficiency is reduced, a large amount of bleaching agent is used, which leads to cost increase and problems such as reduction of pulp viscosity due to radicals and other chemical species generated by decomposition. There is.

[0006] Therefore, as a countermeasure against trace metals, Japanese Patent Laid-Open No.
Japanese Patent No. 148784 discloses a method of bleaching ozone and peroxide, which comprises treating lignocellulose-containing pulp with an acid in the range of pH 1 to 6 and then treating an alkaline earth metal-containing compound with the range of pH 1 to 7. There is. In addition, JP-A-5-1
Japanese Patent No. 48785 discloses a method for bleaching ozone and peroxide in which lignocellulose-containing pulp is treated with a complexing agent of nitrogen polycarboxylic acid within a pH range of 3.1 to 9.0. However, the pretreatment by these methods is
There is a limit to the removal of trace metals and it is not effective.

On the other hand, recently, a method for treating pulp with an enzyme has been studied. Known enzymes are cellulase, xylanase, pectinase, lipase and the like. For example, in JP-B-2-264087, pH 4-8
The method for treating unbleached pulp with an enzyme containing xylanase, and in Japanese Patent Publication No. 2-293486, pH 3 to
In 10, a method for treating unbleached pulp with an enzyme containing hemicellulase has been proposed. But these methods
The delignification effect and the improvement of bleaching property cannot be given at the same time.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art. The delignification reaction is promoted and trace metals can be removed. As a result, low Kappa number and high Provided is a peroxide or ozone bleaching method for chemical pulp, which gives a chemical pulp of whiteness.

[0009]

As a result of intensive studies to solve the above problems, the inventors of the present invention have invented the peroxide or ozone bleaching method for chemical pulp of the present invention.

That is, in the bleaching of chemical pulp with peroxide or ozone, the enzyme and the chelating agent are used before the bleaching treatment, and the treatment is carried out simultaneously in one step or separately in two steps, whereby the delignification reaction by the enzyme is carried out. Is promoted and trace metals are removed by the chelating agent. Therefore, the present invention solves the above problems by a synergistic effect of an enzyme and a chelating agent,
A method for bleaching a peroxide or ozone of a chemical pulp, which can provide a chemical pulp having a low Kappa number and a high whiteness by improving the bleaching property with a peroxide or ozone.

The chemical pulp peroxide or ozone bleaching method of the present invention is carried out by either one-step treatment with a mixture of an enzyme and a chelating agent, or an enzyme treatment followed by a chelating agent treatment, or a chelating agent treatment followed by an enzyme treatment. After bleaching pretreatment consisting of two-stage treatment, peroxide or ozone bleaching is characterized.

The enzyme that can be used in the present invention has the ability to cleave the bond between sugar chains and lignin, or the bond between sugar chains, and is selected from the group of enzymes called hemicellulase or cellulase. Is. Hardwood contains a large amount of xylanase, and an enzyme mainly composed of xylanase is effective. In particular, including xylanase, pH
Those having the maximum activity of 3.5 to 8 are preferable. Examples include Albazyme (GENENCOR), Pulpzyme (NOVO), CT-4 (Amano Pharmaceutical Co., Ltd.) and the like.

Examples of the chelating agent used in the present invention include a chelating agent composed of nitrogen-containing organic or polymeric salt thereof. Specifically, a chelating agent comprising an organic salt such as sodium ethylenediamine tetraacetate (EDTA-Na) and sodium diethylenetriamine pentaacetate (DTPA-5Na), and a chelate comprising a polymer salt such as polyalkylene polyamine polyacetate. Examples thereof include agents. Examples of salts include lithium, sodium and potassium.

As the chemical pulp used in the present invention, unbleached or oxygen-bleached softwood or hardwood is applied.

The conditions for the one-step or two-step pre-bleaching pretreatment using the enzyme of the present invention and the chelating agent are as follows.

The pulp concentration is 2 to 15% by weight, preferably 3 to 12% by weight. Here, if the pulp concentration is less than 2% by weight, the treatment efficiency is poor, and if the pulp concentration is more than 15% by weight, stirring and mixing are insufficient, which is not preferable.

In the case of xylanase, the amount of enzyme added is
0.1 to 1000 u / g (vs pulp), preferably 1 to
100 u / g (vs pulp). Here, if the amount of enzyme added is less than 0.1 u / g (vs. pulp), there is no treatment effect,
When it exceeds 1000 u / g (vs. pulp), the yield and the viscosity are drastically reduced.

The amount of the chelating agent added is 0.01 to 5% by weight, preferably 0.05 to 3% by weight, based on the pulp. Here, if the amount of chelate added is less than 0.01% by weight, there is almost no treatment effect, and if it exceeds 5% by weight, the effect is insufficient and it is economically disadvantageous.

The processing temperature is 30 to 80 ° C., preferably 4
It is 0 to 70 ° C. Here, if the treatment temperature is lower than 30 ° C, the treatment efficiency is slow, and if it exceeds 80 ° C, the effect of the enzyme does not appear.

The treatment time is 30 to 180 minutes, preferably 60 to 120 minutes. Here, if the processing time is less than 30 minutes, the effect is small, and if it is longer than 180 minutes, no further effect appears.

The treatment pH is 4-8, preferably 4.5-.
It is 7.5. Here, when the treatment pH is less than 3.5 or higher than 8, the effect of the enzyme does not appear.

The xylanase activity is 1 u / l of 1% xylan (about pH 5) and 1 ml of enzyme, which produce a reducing power corresponding to 1 μmol xylose per minute when they are allowed to act at 50 ° C. for 30 minutes. Expressed as g (vs pulp).

The peroxide used in the present invention is, for example,
Examples thereof include organic peroxides such as benzoyl peroxide and peracetic acid, and inorganic peroxides such as hydrogen peroxide, sodium peroxide and monosulfuric acid peroxide.

After the bleaching pretreatment, the bleaching conditions of the chemical pulp with peroxide are as follows.

The amount of peroxide added is 0.1 to 3.0% by weight, preferably 0.5 to 2.0% by weight, calculated as hydrogen peroxide. Here, if the added amount of peroxide is less than 0.1% by weight, there is almost no effect, and if it exceeds 3.0% by weight, the effect is not sufficient and it is economically disadvantageous.

The reaction temperature is 30 to 100 ° C, preferably 40 to 90 ° C. Here, when the reaction temperature is lower than 30 ° C., the treatment efficiency is slow, and when it exceeds 100 ° C., it is difficult in terms of equipment.

The reaction time is 30 to 240 minutes, preferably 40 to 180 minutes. Here, if the reaction time is less than 30 minutes, the effect is small, and if the reaction time is longer than 240 minutes, no further effect appears.

The reaction pH is 8 to 13, preferably pH 9
~ 12.5. Here, if the reaction pH is less than 8, there is almost no effect, and if the reaction pH is higher than 13, the effect is not sufficient and it is economically disadvantageous.

The pulp concentration is 2 to 15% by weight, preferably 3 to 12%. Here, if the pulp concentration is less than 2% by weight, the treatment efficiency is poor, and if the pulp concentration is more than 15% by weight, stirring and mixing are insufficient, which is not preferable.

After the bleaching pretreatment, the bleaching conditions of the chemical pulp with ozone are as follows.

The amount of ozone added is 0.01 to 10.0% by weight, preferably 0.1 to 5% by weight. Here, if the amount of ozone added is less than 0.01% by weight, there is almost no effect, and if it exceeds 10% by weight, the effect is not sufficient and it is economically disadvantageous.

The reaction temperature is 10 to 100 ° C, preferably 20 to 90 ° C. Here, if the reaction temperature is lower than 10 ° C, the treatment efficiency is slow, and if it exceeds 100 ° C, it is difficult in terms of equipment.

The reaction time is 1 to 120 minutes, preferably 5 minutes.
~ 60 minutes. Here, if the reaction time is less than 1 minute, the effect is small, and if it is longer than 120 minutes, no further effect appears.

The reaction pH is 1 to 5, preferably pH 1.
5 to 4. Here, if the reaction pH is less than 1, the effect is insufficient, and if the reaction pH is higher than 5, the effect is scarce.

The pulp concentration is 2 to 40% by weight, preferably 3 to 35% by weight. Here, if the pulp concentration is less than 2% by weight, the treatment efficiency is poor, and if the pulp concentration is more than 40% by weight, stirring and mixing are insufficient, which is not preferable.

The washing solution obtained by the bleaching pretreatment and the peroxide or ozone bleaching treatment can be countercurrently returned to the preceding processing stage and finally sent to the black liquor recovery step.

After bleaching the chemical pulp with peroxide or ozone, it can be bleached by any of the bleaching methods described below. A method of bleaching in an aqueous medium using chlorine dioxide and hypochlorite. A method of bleaching with an ozone in an aqueous medium or with a gas. A method of bleaching in an alkaline aqueous medium using a peroxide or a peroxide and oxygen. A method of bleaching in an alkaline aqueous medium using thiourea dioxide.

[0038]

According to the present invention, the delignification reaction is promoted by the enzyme by the simultaneous treatment with the enzyme and the chelating agent in one step or each of the two steps before bleaching the peroxide or ozone of the chemical pulp. Removes trace metals. Therefore, it is possible to maximize the effects of peroxide and ozone by the synergistic effect of the enzyme and the chelating agent, and to significantly reduce the amount of peroxide or ozone added. Furthermore, since there is no chlorine drainage in the previous stage, not only is the drainage load reduced, but it also leads to the reduction of environmentally problematic organic chlorine compounds. It is also possible to reuse white water.

[0039]

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In the examples, all parts and% are parts by weight and% by weight.
It is due to. The whiteness is JIS-P8123.
(Hunter whiteness method), pulp viscosity is TAPPI T
-230 om-82, Kappa price is TAPPIT-
It was measured by the method of 236 hm-85.

Example 1 Unbleached pulp of domestic hardwood (kappa number 9.1, viscosity 2)
3.7 cp, whiteness 44.7%), 10 u / g of xylanase having an optimum pH of 5 to 7 (to pulp) as an enzyme and 0.1% of Na salt of polyalkylene polyamine polyacetate as a chelating agent are added at the same time. After mixing, the pH was adjusted to 5.0 with sulfuric acid and the pulp concentration was 10%, and the mixture was reacted at 60 ° C. for 2 hours. After that, it is washed and dehydrated, and hydrogen peroxide (hereinafter,
H ₂ O ₂ ) 1.0%, sodium hydroxide (hereinafter,
1.3% of NaOH) was added to adjust the pulp concentration to 12%, and the oxygen reaction pressure was 2 kg / cm ² , and the temperature was 1.5 at 60 ° C.
Bleached for hours. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Example 2 The same unbleached pulp as in Example 1 was mixed with 10 u / xylanase.
g (against pulp) and as a chelating agent, sodium diethylenetriamine pentaacetate (hereinafter referred to as DTPA-Na)
0.1% was added and mixed at the same time, pH was adjusted to 5.0 with sulfuric acid and pulp concentration was 10%, and the mixture was reacted at 60 ° C. for 2 hours.
Then, it was washed and dehydrated, and H ₂ O ₂ 1.0%, NaOH 1.
The pulp concentration was adjusted to 12% by adding 3%, and the pulp was bleached for 1.5 hours at 60 ° C. under an oxygen reaction pressure of 2 kg / cm ² . After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Example 3 The same unbleached pulp as in Example 1 was mixed with 10 u / xylanase.
g (vs pulp) was added, the pH was adjusted to 6.0 with sulfuric acid and the pulp concentration was 10%, and the mixture was reacted at 60 ° C. for 2 hours. Then, it was washed and dehydrated, and 0.1% Na salt of polyalkylene polyamine polyacetate was added as a chelating agent to prepare a pulp concentration of 3.5%, and the mixture was reacted at 55 ° C. for 40 minutes. After the reaction, wash and dehydrate, H ₂ O ₂ 1.0%, NaOH
The pulp concentration was adjusted to 12% by adding 1.3%, and bleaching was performed at 60 ° C. for 1.5 hours at an oxygen reaction pressure of 2 kg / cm ² . After bleaching, wash and measure whiteness, kappa number, and viscosity,
The results are shown in Table 1.

Example 4 The same unbleached pulp as in Example 1 was prepared by using as a chelating agent, a sodium salt of polyalkylene polyamine polyacetate 0.1.
% To prepare a pulp concentration of 3.5%, and add 40% at 55 ° C.
Let react for minutes. Then, it is washed and dehydrated, and xylanase 1
0 u / g (vs pulp) was added and the pH was adjusted to 6.0 with acetic acid,
The pulp concentration was adjusted to 10%, and the mixture was reacted at 60 ° C. for 2 hours. After the reaction, wash and dehydrate, H ₂ O ₂ 1.0%, NaOH
The pulp concentration was adjusted to 12% by adding 1.3%, and bleaching was performed at 60 ° C. for 1.5 hours at an oxygen reaction pressure of 2 kg / cm ² . After bleaching, wash and measure whiteness, kappa number, and viscosity,
The results are shown in Table 1.

Example 5 The same unbleached pulp as in Example 1 was mixed with 1 u / g of xylanase.
(To pulp) and 1.0% of Na salt of polyalkylene polyamine polyacetate as a chelating agent are added and mixed at the same time, pH is adjusted to 5.5 with sulfuric acid and pulp concentration is 10%, and reacted at 60 ° C. for 2 hours. It was After that, wash and dehydrate,
H ₂ O ₂ 1.0% and NaOH 1.3% were added to adjust the pulp concentration to 12%, and the oxygen reaction pressure was 2 kg / cm ² , 60.
Bleached at 1.5 ° C. for 1.5 hours. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Example 6 The same bleached pulp as in Example 1 was mixed with xylanase 1200.
u / g (against pulp) and 0.01% Na salt of polyalkylene polyamine polyacetate as a chelating agent are added and mixed at the same time, pH is 5.5 with sulfuric acid, and pulp concentration is 10%.
And was reacted at 60 ° C. for 2 hours. Then, it was washed and dehydrated, and H ₂ O ₂ 1.0% and NaOH 1.3% were added to adjust the pulp concentration to 12%, and the oxygen reaction pressure was 2 kg / cm.
^2. Bleached at 60 ° C for 1.5 hours. After bleaching, wash,
The whiteness, Kappa number, and viscosity were measured, and the results are shown in Table 1.

Example 7 To the unbleached pulp of Example 1, 10 u / g of xylanase (against pulp) and 0.1% of Na salt of polyalkylene polyamine polyacetate as a chelating agent were simultaneously added and mixed, and the pH was adjusted with sulfuric acid. A pulp sample prepared to have a pulp concentration of 6.0 and a pulp concentration of 10% was reacted at 60 ° C. for 2 hours. Then, after washing and dehydration to adjust the pulp concentration to 15%, the pH is adjusted to 2 with sulfuric acid.
Adjust to. 0.5% of ozone was added using a tester of a medium-concentration ozone bleaching apparatus, and bleaching was performed at 25 ° C. for 5 minutes. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Example 8 The same unbleached pulp as in Example 1 was mixed with 10 u / xylanase.
g (vs. pulp) and diethylenetriamine sodium pentaacetate (DTPA-5Na) 0.1% were added and mixed at the same time,
The pH was adjusted to 6.0 with sulfuric acid and the pulp concentration was 10%.
The reaction was carried out at 0 ° C for 2 hours. Then, after washing and dehydration to adjust the pulp concentration to 15%, the pH is adjusted to 2 with sulfuric acid. 0.5% ozone by using a test machine of medium concentration ozone bleaching equipment
It was added and bleached at 25 ° C. for 5 minutes. After bleaching,
After washing, whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Example 9 The same unbleached pulp as in Example 1 was mixed with 10 u / xylanase.
g (vs pulp) was added, the pH was adjusted to 6.0 with sulfuric acid and the pulp concentration was 10%, and the mixture was reacted at 60 ° C. for 2 hours. Then, it is washed and dehydrated, 0.1% Na salt of polyalkylene polyacetate is added as a chelating agent, and the pulp concentration is 3.
It was adjusted to 5% and reacted at 55 ° C. for 40 minutes. After the reaction
After washing and dehydration to adjust the pulp concentration to 15%, p
Adjust to H2. 0.5% of ozone was added using a tester of a medium-concentration ozone bleaching apparatus, and bleaching was performed at 25 ° C. for 5 minutes. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Example 10 To the same unbleached pulp as in Example 1 was added 0.1% Na salt of polyalkylene polyacetate as a chelating agent.
The pulp concentration was adjusted to 3.5%, and the mixture was reacted at 55 ° C. for 40 minutes. Then, it was washed and dehydrated, xylanase 10 u / g (to pulp) was added, the pH was adjusted to 6.0 with sulfuric acid, and the pulp concentration was 1
It was adjusted to 0% and reacted at 60 ° C. for 2 hours. After the reaction, wash and dehydrate to adjust the pulp concentration to 15%, then add pH with sulfuric acid.
Adjust to 2. 0.5% of ozone was added using a tester of a medium-concentration ozone bleaching apparatus, and bleaching was performed at 25 ° C. for 5 minutes. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Example 11 Unbleached pulp similar to that of Example 1 was mixed with 1 u / g of xylanase.
(To pulp) and 1.0% of Na salt of polyalkylene polyamine polyacetate as a chelating agent are added and mixed at the same time, pH is adjusted to 6.0 with sulfuric acid and pulp concentration is 10%, and reacted at 60 ° C. for 2 hours. It was After that, wash and dehydrate,
After adjusting the pulp concentration to 15%, the pH is adjusted to 2 with sulfuric acid. 0.5% of ozone was added using a tester of a medium-concentration ozone bleaching apparatus, and bleaching was performed at 25 ° C. for 5 minutes. After bleaching, wash and measure whiteness, kappa number, and viscosity,
The results are shown in Table 1.

Example 12 The same bleached pulp as in Example 1 was mixed with xylanase 1200.
u / g (vs pulp) and 0.01% Na salt of polyalkylene polyamine polyacetate as chelating agent are added and mixed at the same time, pH is 6.0 with sulfuric acid, pulp concentration is 10%
And was reacted at 60 ° C. for 2 hours. Then, after washing and dehydration to adjust the pulp concentration to 15%, the pH is adjusted to 2 with sulfuric acid. 0.5% of ozone was added using a tester of a medium-concentration ozone bleaching apparatus, and bleaching was performed at 25 ° C. for 5 minutes. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Comparative Example 1 The same unbleached pulp as in Example 1 was mixed with 1.0% H ₂ O ₂ and N _2.
1.3% aOH was added to prepare a pulp concentration of 12%, and bleaching was carried out at 60 ° C. under an oxygen reaction pressure of 2 kg / cm ² for 1.5 hours. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Comparative Example 2 To the same unbleached pulp as in Example 1, 10 u / g of xylanase (against pulp) was added as an enzyme, the pH was adjusted to 6.0 with sulfuric acid and the pulp concentration was 10%, and the temperature was 60 ° C. And reacted for 2 hours. After the reaction, the product was washed and dehydrated, H ₂ O ₂ 1.0%, N
1.3% aOH was added to prepare a pulp concentration of 12%, and bleaching was carried out at 60 ° C. under an oxygen reaction pressure of 2 kg / cm ² for 1.5 hours. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Comparative Example 3 An unbleached pulp similar to that used in Example 1 was prepared by using as a chelating agent, a sodium salt of polyalkylene polyamine polyacetate of 0.1.
% To prepare a pulp concentration of 3.5%, and add 40% at 55 ° C.
Let react for minutes. After the reaction, it was washed and dehydrated, and H ₂ O ₂ 1.0
% And NaOH 1.3% to prepare a pulp concentration of 12%, and bleaching was carried out at 60 ° C. for 1.5 hours at an oxygen reaction pressure of 2 kg / cm ² . After bleaching, wash, whiteness, kappa value,
The viscosity was measured and the results are shown in Table 1.

Comparative Example 4 To the same unbleached pulp as in Example 1, 0.1% of sodium diethylenetriaminepentaacetate (DTPA-5Na) was added to prepare a pulp concentration of 3.5%, and the mixture was reacted at 55 ° C. for 40 minutes. It was After the reaction, the product was washed and dehydrated, H ₂ O ₂ 1.0%, N
1.3% aOH was added to prepare a pulp concentration of 12%, and bleaching was carried out at 60 ° C. for 1.5 hours at an oxygen reaction pressure of 2 kg / cm ² . After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Comparative Example 5 To the same unbleached pulp as in Example 1, 1% sulfuric acid was added to prepare a pulp concentration of 3.5%, and the pulp was reacted at 55 ° C. for 40 minutes. After the reaction, wash and dehydrate, H ₂ O ₂ 1.0%, NaOH
The pulp concentration was adjusted to 12% by adding 1.3%, and bleaching was performed at 60 ° C. for 1.5 hours at an oxygen reaction pressure of 2 kg / cm ² . After bleaching, wash and measure whiteness, kappa number, and viscosity,
The results are shown in Table 1.

Comparative Example 6 The same unbleached pulp as in Example 1 was prepared to a pulp concentration of 15%, and then adjusted to pH 2 with sulfuric acid. Add 0.5% ozone using a tester of medium concentration ozone bleaching equipment,
Bleached for 5 minutes. The bleached pulp was washed and measured for whiteness, kappa number and viscosity, and the results are shown in Table 1.

Comparative Example 7 To the same unbleached pulp as in Example 1, 10 u / g of xylanase (against pulp) was added as an enzyme, the pH was adjusted to 5.0 with sulfuric acid and the pulp concentration was 10%, and the temperature was 60 ° C. And reacted for 2 hours. After the reaction, the product is washed and dehydrated to adjust the pulp concentration to 15%, and then adjusted to pH 2 with sulfuric acid. Add 0.5% of ozone using a test machine of medium concentration ozone bleaching equipment,
Bleaching was carried out under conditions of 5 ° C. and 5 minutes. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Comparative Example 8 The same unbleached pulp as in Example 1 was prepared by using, as a chelating agent, Na salt of polyalkylene polyamine polyacetate of 0.1.
% To prepare a pulp concentration of 3.5%, and add 40% at 55 ° C.
Let react for minutes. After the reaction, washing and dehydration, pulp concentration 15
%, And then adjusted to pH 2 with sulfuric acid. 0.5% of ozone was added using a tester of a medium-concentration ozone bleaching apparatus, and bleaching was performed at 25 ° C. for 5 minutes. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

Comparative Example 9 Sodium diethylenetriaminepentaacetate (DTPA-5N) was used as a chelating agent in the same unbleached pulp as in Example 1.
a) Add 0.1% to prepare a pulp concentration of 3.5%, and
The reaction was carried out at 5 ° C for 40 minutes. After the reaction, the product is washed and dehydrated to adjust the pulp concentration to 15%, and then adjusted to pH 2 with sulfuric acid.
Ozone was neutralized using a test machine of a medium concentration ozone bleaching device.
5% was added and bleaching was carried out at 25 ° C. for 5 minutes. After bleaching, it was washed and the whiteness, kappa number and viscosity were measured, and the results are shown in Table 1.

[0061]

[Table 1]

From Examples 1 to 12 and Comparative Examples 1 to 9 in Table 1, the present invention treats the enzyme, the chelating agent and the acid alone or in a single step, compared to the conventional method in which they are not added. Alternatively, it can be seen that a chemical pulp having a low Kappa number and a high whiteness can be obtained by treating the enzyme and the chelating agent in two stages of the enzyme and the chelating agent. However, the simultaneous treatment method in the first stage is excellent in efficiency although there is almost no difference in whiteness and Kappa number in the two stages compared to the respective treatments.

[0063]

Industrial Applicability According to the present invention, a chemical pulp having a low Kappa number and a high whiteness can be obtained as compared with the conventional peroxide or ozone bleaching method. Furthermore, since there is no chlorine drainage in the previous stage, not only is the drainage load reduced, but it also leads to the reduction of environmentally problematic organic chlorine compounds. It is also possible to reuse white water.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Nakamura 3-4-2 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Paper Mills Co., Ltd.

Claims (11)

[Claims] 1. A method of peroxide or ozone bleaching of chemical pulp, which comprises a one-step treatment with a mixture of an enzyme and a chelating agent, or an enzyme treatment followed by a chelating agent treatment, and a chelating agent treatment followed by an enzyme treatment. A method for bleaching peroxide or ozone in chemical pulp, which comprises bleaching peroxide or ozone after pretreatment for bleaching, which comprises a step treatment. 2. After the bleaching pretreatment, washing with a washing solution containing a dehydrated washing solution from a chlorine-free bleaching stage, and bleaching with peroxide or ozone is carried out, and Oxide or ozone bleaching methods. 3. The method for bleaching peroxide or ozone for chemical pulp according to claim 1, wherein after the pre-bleaching treatment, washing with warm water is carried out to bleach peroxide or ozone. 4. The method for bleaching peroxide or ozone of chemical pulp according to claim 1, wherein the enzyme is an enzyme containing xylanase. 5. The chemical pulp peroxide or ozone bleaching method according to claim 1, wherein the chelating agent is a chelating agent comprising a nitrogen-containing organic salt or a polymer salt thereof. 6. The chemical pulp comprises unbleached or oxygen-bleached softwood or hardwood.
A method for bleaching a peroxide or ozone of a chemical pulp as described. 7. As conditions for the bleaching pretreatment, a pulp concentration is 2 to 15% by weight, and an enzyme addition amount of xylanase activity is 0.
1 to 1000 u / g (relative to pulp), the amount of chelating agent added is 0.01 to 5% by weight, the treatment temperature is 30 to 80 ° C., the treatment time is 30 to 180 minutes, and the treatment pH is 4 to 8. The method for bleaching peroxide or ozone of chemical pulp according to claim 1. 8. After the bleaching pretreatment, as a bleaching condition with a peroxide, a pulp concentration is 2 to 15% by weight, a peroxide addition amount is 0.1 to 3.0% by weight in terms of hydrogen peroxide, The peroxide or ozone bleaching method of chemical pulp according to claim 1, wherein the reaction temperature is 30 to 100 ° C, the reaction time is 30 to 240 minutes, and the reaction pH is 8 to 13. 9. After bleaching pretreatment, as a bleaching condition with ozone, pulp concentration is 2 to 40% by weight, ozone addition amount is 0.01 to 10.0% by weight, and reaction temperature is 10 to 10%.
The peroxide or ozone bleaching method for chemical pulp according to claim 1, wherein the reaction time is 1 to 120 minutes at 0 ° C, and the reaction pH is 1 to 5. 10. The cleaning solution according to the bleaching pretreatment and the peroxide or ozone bleaching treatment is countercurrently returned to the preceding treatment stage and finally sent to the black liquor recovery step. Method of peroxide or ozone bleaching of chemical pulp. 11. After bleaching the chemical pulp with peroxide or ozone, the bleaching method according to any one of the following:
The method for bleaching peroxide or ozone of chemical pulp according to claim 1, wherein the method is bleaching. A method of bleaching in an aqueous medium using chlorine dioxide and hypochlorite. A method of bleaching with an ozone in an aqueous medium or with a gas. A method of bleaching in an alkaline aqueous medium using a peroxide or a peroxide and oxygen. A method of bleaching in an alkaline aqueous medium using thiourea dioxide.